The physical layer is the first and lowest layer in the seven-layer open systems interconnection (OSI) model of computer networking, and it provides certain communication foundations for wireless communications using the IEEE 802.11 standards, IEEE Std. 802.11-2007, published in 2007. The implementation of the physical layer is often termed PHY; however, the physical layer itself includes the basic hardware transmission technologies of a network, and defines how raw bits are transmitted over a network. The bit stream may be grouped into code words or symbols and converted to a physical signal for transmission over a hardware transmission medium. The physical layer provides an electrical, mechanical, and procedural interface to the transmission medium, including the broadcast frequencies and the modulation schemes.
Wireless connectivity for computers is now well-established and virtually all new laptops contain a Wi-Fi capability. Of the wireless local area network (WLAN) solutions that are available, the IEEE 802.11 standard, often termed Wi-Fi, has become the de-facto standard. By using the IEEE 802.11 standards, system operating speeds of around 54 Mbps are commonplace and Wi-Fi is able to compete well with wired systems. Wi-Fi hotpots are in common use, and they allow communications without cable connections. Some of the established IEEE 802.11 standards may provide wireless connectivity for common devices such as laptops and smartphones. However, high bandwidth communications protocols may not be ideal for Internet connectivity with certain devices, such as small, battery-powered sensors that may have limited battery capacity, that may require extended wireless link ranges, or that do not need to communicate at high data rates.
The IEEE 802.11ah task group was recently formed to provide an orthogonal frequency-division multiplexing (OFDM) system operating in the 1 GHz and lower bands. One of the goals of the IEEE 802.11ah task group is to reuse the IEEE 802.11n/ac system with new features that meet certain criteria, including long range, low data rate service (for long-range sensors, for example). Therefore, systems having bandwidths of approximately 1 to 16 MHz are being investigated for use with IEEE 802.11ah. These bandwidths may be provided by down-clocking the IEEE 802.11ac system; however, not all of the requirements for providing service may be met without additional modifications to the IEEE 802.11ac PHY structure.